a. Field of the Invention
The present invention refers to a process and apparatus for the preparation of intermediates of polyaddition and polycondensation resins. These are plastics which are prepared by the polyaddition reaction of one ore more resin precursors together with hardener and any other ingredients. The resultant intermediate resin then being obtained as a fine powder, wherein the resin macromolecules are not yet cross-linked, or have been allowed under control to develop the so-called partial cross-links only. This means of course that the most reactive hardener has not yet reacted, allowing the powder to be applied for example as thin homogenous layer to an object and then to be melt-fused to a homogenous coating, which is fully hardened, or respectively that the powder can be fused to desired form in a heated die resulting in fully hardened parts.
At least one of the resin precursors is a linear polymer, which by itself may not be hardenable, but which can accept in a polymeric addition reaction further monomers or polymers. The reaction proceedsstepwise and intermediate products show properties which progress from completely fuseable over partially fuseable to completely hardened and thermoset. The more important physical properties change as well, especially the melt viscosity and the brittleness. Nevertheless, highly reactive components remain in the intermediate products, sensitive to react under influence of temperature and sometimes also of pressure, though to a more limited extent.
The intermediates furthermore do not possess a sharply defined melting point and depending on the intermediate stage they have frequently a very broad melting range.